Gelled chromium acetate cross-linked aqueous slurry type salt explosives, and manufacture

ABSTRACT

Gelled aqueous slurry salt type explosives in which the gelation agent is guar gum crosslinked with a chromium acetate at pH levels lower than heretofore, viz, at 4.5-5.4, by crosslinking the guar gum in the pH range with a chromium acetate of the group of chromium hydroxy acetate, chromium triacetate, and mixtures thereof, in the presence of calcium nitrate which constitutes at least part of the oxidizer salt. Heretofore, guar gum/chromium acetate gelation agents for the above explosives have been available only at higher pH levels with accompanying impairment of gel strength and stability, water resistance, viscosity characteristics, and stability of certain ingredients of the explosive.

United States Patent 1191 Knight, Jr.

[ Mar. 19, 1974 GELLED CHROMIUM ACETATE CROSSLINKED AQUEOUS SLURRY TYPE SALT EXPLOSIVES, AND MANUFACTURE [75] Inventor: Herbert G. Knight, Jr., Succasunna,

[73] Assignee: Hercules Incorporated, Wilmington,

Del.

22 Filed: Mar. 26, 1973 21 Appl. No.: 345,161

52 U.S. Cl 149/60, 149/41, 149/44,

149/61 51 1111.0 ..C06b1/04 [58] Field of Search 149/44, 41, 60, 61

[56] References Cited UNITED STATES PATENTS 9/1967 Desmarcos 149/41 X 4/1972 Fee et a1. l49/4l X Primary ExaminerStephen J. Lechert, Jr. Attorney, Agent, or Firm-S. Grant Stewart [5 7] ABSTRACT Heretofore, guar gum/chromium acetate gelation agents for the above explosives have been available only at higher pH levels with accompanying impairment of gel strength and stability, water resistance, viscosity characteristics, and stability of certain ingredients of the explosive.

13 Claims, N0 Drawings GELLED CHROMIUM ACETATE CROSS-LINKED AQUEOUS SLURRY TYPE SALT EXPLOSIVES, AND MANUFACTURE This invention relates to gelled aqueous slurry salt explosives containing an improved gelation system In another embodiment this invention relates to the manufacture of the above described explosives. Other aspects will be apparent in light of the accompanying disclosure and the appended claims.

Salt type explosives of the aqueous slurry type include the oxidizer salt, water and sensitizer components, often with a thickener and one or more of supplemental fuel, salt and energizing ingredients, and have had extensive use in recent years. These aqueous slurry explosives are often cap sensitive, although generally they are not detonatable by direct action of a No. 8 commercial blasting cap, but they are detonatable in response to action of a suitable booster charge.

in such slurry type explosives, the sensitizer is generally smokeless powder, a high explosive such as TNT or PETN, or a nonexplosive such as particulate aluminum, DNT oil and the like; and, in numerous instances, gas bubbles are present to enhance sensitivity. A separate fuel component is often utilized for suitable oxygen balance and to provide supplemental energy properties. Generally, the explosive contains a gelation agent as a thickener component, often in crosslinked form and in at least a sufficient amount to cause the slurried ingredients to be retained in aqueous suspension. The oxidizer salt component is of the inorganic oxidizer and/or oxidizer-fuel types, exemplary of which are alkali metal, ammonium, and alkaline earth metal nitrates, and alkylamine nitrates, respectively.

Guar gum has been widely used as a gelation agent for the above described salt type explosives, generally crosslinked with a suitable crosslinking agent exemplary of which are those of US. Pat. No. 3,301,723. Although chromium salts have been proposed as crosslinking agents for guar gum in the above salt type explosives, they have been utilized at pH levels of 6 and higher as set forth in US. Pat. No. 3,301,723. However, l have found that due to those high pH conditions various properties of the explosives product are impaired, particularly gel strength and stability, and stability of certain ingredients of the explosive.

This invention is based on my discovery that gelled aqueous slurry salt explosives containing guar gum crosslinked with a chromium acetate(s) of a selected class can be prepared at significantly lower pH levels than heretofore, under which conditions the resulting explosive product exhibits markedly improved stability, water resistance, and viscosity characteristics.

In accordance with the invention, aqueous slurry salt type explosives containing guar gum crosslinked with a chromium acetate, as a gelation agent, are provided, which comprise calcium nitrate as at least part of the oxidizer salt component, and as said gelation agent guar gum crosslinked in the presence of at least part of said calcium nitrate at a pH of from about 4.5 to 5.4 with a chromium acetate of the group of chromium hydroxy diacetate, chromium triacetate, and mixtures thereof.

Further in accordance with the invention, a method for manufacture of a gelled aqueous salt slurry type explosive above described is provided, which comprises incorporating calcium nitrate into said explosive as at least part of the oxidizer salt, and effecting the gelation by crosslinking said guar gum with said chromium acetate in the presence of at least part of said calcium nitrate within said pH range of from 4.5 to 5.4.

The degree of the crosslinking can be varied over a broad range by regulating the amounts of guar gum and chromium acetate crosslinking agent incorporated into the formulation, and particularly when the amount of calcium nitrate present during the crosslinking reaction is at least about 5 percent, based on the weight of the explosive. Generally, based on the weight of the explosive, from about 0.1 to 1.5 percent guar gum is crosslinked with from about 0.01 to 0.5 percent of the chromium acetate. When the guar gum and chromium acetate contents are within the respective ranges of 0.4 to 1.5 percent, and 0.05 to 0.50 percent, the consistency of the gelled explosive product is variable over a range of from difficultly pumpable to unpumpable; and when smaller proportions of the guar gum and chromium acetate crosslinking agent are utilized, the product consistency is easily varied from pumpable to readily pourable.

Regulation of rate of the guar gum-chromium acetate cross-linking reaction can be increased by raising the crosslinking reaction temperature from ambient levels to as high as F. and higher; and the crosslinking rate can be lowered by lowering the reaction temperature from ambient temperature levels, and/or by the presence of acetate ion at any desired temperature level, preferably supplied by sodium acetate or acetic acid introduced into the crosslinking reaction system in an amount of from about 0.01 to 2.0 weight percent of the explosive.

The invention, due to the unique characteristics of the particular chromium acetates in respect of their behavior in the presence of calcium nitrate to accomplish the gelation at a pH of 5.4 and lower, provides for improved stability of the explosive from the standpoint of gel strength, gel stability, water resistance and im' proved viscosity characteristics; and it also provides for the use of chromium acetate-guar gum gelation systems in formulations which can only exhibit maximum stability of certain of the ingredients when the pH level of the explosive is markedly lower than 6. The invention is therefore particularly advantageously applied to those formulations containing metallic energizers such as aluminum, and those formulations in which density is controlled by the addition of gassing agents such as sodium nitrite, sodium carbonate, and others, which require pH levels not exceeding about 5 to 5.4 for maximum stability.

Exemplary oxidizer salts utilized in the practice of the invention, in addition to the calcium nitrate required in all embodiments, include inorganic oxidizer salts such as alkali metal and alkaline earth metal nitrates and perchlorates such as, for example, sodium nitrate, magnesium nitrate, potassium nitrate, barium nitrate, sodium perchlorate, ammonium perchlorate, calcium perchlorate and magnesium perchlorate; and organic salt components such as nitrogen based oxidizer fuel salts including hexamethylene-tetramine monoor di-nitrates, primary, secondary and tertiary alkyl, and alkanol, amine nitrates, generally containing one to four carbon atoms in each alkyl, or alkanol group, as for example, monomethylamine nitrate, dimethylamine nitrate, timethylamine nitrate, monoethylamine nitrate, diethylamine nitrate, triethylamine nitrate, monopropylamine nitrate, dipropylamine nitrate, tripropylamine nitrate, monobutylamine nitrate, dibutylamine nitrate, tributylamine nitrate, monoethanolamine nitrate, diethanolamine nitrate, triethanolamine closed in U.S. Pat. No. 3,653,992. Other suitable sensitizers include particulate magnesium-aluminum alloys, and high explosives such as PETN, tetryl, and the like.

Formulations contain nonexplosive fuels, as for exnitrate, and the like. 5 ample ethylene glycol, are advantageously employed in Particle size of the salt ingredients, which are norpractice of the invention. Nonsoluble fuels such as mally solid, is generally not critical. For example. amground coal, powdered sulfur, fuel oil and other hydromonium nitrate can consist of prills such as used in fercarbons are also useful when suitably dispersed. Genertilizers or it can be granular and in form varied from ally, the amount of fuel, including inorganic and/or incoarse to fine, and when desired, all or any portion of organic fuel-sensitizer, is in the order of from about it can be added to the slurry formulation in aqueous 80- 2-50 percent. lution. The oxidizer salt component can be solely inor- The gelled explosive compositions of the invention ganic, or, except for the calcium nitrate, it can be solely are exemplified by those of the following formulations:

Weight Percent Example No. l 2 3 4 Water 250 17.1 l 22.0 9.3 Ammonium Nitrate 21.37 36.40 26.3 53.92 Calcium Nitrate 21.36 16.50 26.3 10.0

Sodium Nitrate 500 Ethylene Glycol Mononitrate 14.40 10.30 9.0 9.0 Ethylene Glycol 10.00 4.80 10.0 6.0 Guar Gum 0.25 0.50 0.6 0.4 Chromium Acetate" 0.02 0.21 0.1

Chromium Triacetate 0.2 Zinc Oxide 0.5 0.5 0.5 0.25

Pine Oil 0.1 0.1 Glass Microballons 2.0 3.4 1.0

Perlite 5.0 Aluminum 10.0 10.0

Sodium Acetate 0.1 0.01 Acetate Acid 0.18 0.02

Type of Slurry Pourable Firm Gel Firm Gel Firm Gel l 96" Funnel Test (2000 cm) 8 secs pH 5.0 4.9 4.9 5.0 Crosslinking time at 140F. 1 hr. about 1 min. mins. Ingredient Separation after None None None None one month at 120F.

All of the above formulations shoot with detonation rates in excess of 4000 m/sec. when tested in a 4" diameter unconfined bag with a 1 lb. cast booster.

(I) a mixture of 2 mols of chromium hydroxy diacetate (Cr(OH)AC,) and 1 mol of chromium triacetate (CrAC AC"=acetatc. (2) Funnel Test-Approximately 2 liters of slurry is poured into an aluminum funnel having an orifice of varied diameter. When the orifice is opened to permit flow. the timing is started. When light is visible through the orifice (looking down into the funnel), timing is stopped.

organic; or it can constitute a mixture of organic and inorganic salts either one of which can be in major proportion.

The explosive compositions of the invention contain, as the now preferred oxidizer salt component, from about 5 to percent of the calcium nitrate, and additionally from about 10 to 80 percent ammonium nitrate alone or with a supplemental salt such as sodium nitrate. The calcium nitrate content of the oxidizer salt component is generally at least about 10 percent, and it can constitute all or any greater proportion of the oxidizer salt, as desired.

The gelled explosives of the invention are detonatable in response to direction action of either a commercial No. 8 blasting cap or a conventional booster charge such as PETN (pentaerythritol tetranitrate), RDX (cyclotrimethylenetrinitramine), RDX (cyclotrimethylenetrinitramine), Pentolite (PETN-TNT), tetryl, Composition B (RDX-TNT), and the like, dependent on the particular sensitizer system.

Any of the various known sensitizer materials for inorganic oxidizer salt blasting compositions of the aqueous slurry type, above described, can be utilized as such, in the compositions of the invention. Exemplary of now preferred sensitizer components are smokeless powder as disclosed in U.S. Pat. No. 3,235,425, TNT and/or particulate aluminum as disclosed in U.S. Pat. No. 2,930,685, and ethylene glycol mononitrate as dis- The above formulations illustrate a chromium hydroxy diacetate/chromium triacetate mixture, and chromium triacetate alone, as crosslinking agents with guar gum in gelation system of the explosives of the invention. Examples 2 and 4 illustrate the use of an acetic acid-sodium acetate blend to lower the cross-linking rate; Example 1 illustrates a combination of low guar gum content and crosslinking agent for relative low consistency to form a pourable slurry product; and Examples 2 and 4 illustrate aluminum-containing formulations which, in contrast to similar formulations utilizing chromium salt/guar gum gelation systems of the prior art, are at substantially maximum stability.

Any suitable method can be utilized in the prepara tion of the explosive compositions of the invention. Thus, by way of example the explosive composition of Example 2 is formed in accordance with the following procedure:

Ethylene oxide is reacted with aqueous nitric acid to form ethylene glycol mononitrate as described in U.S. Pat. No. 3,653,992, the resulting aqueous solution containing, on a weight basis, 36 percent ethylene glycol mononitrate, 24 percent ammonium nitrate, 30 percent water and 10 percent ethylene glycol by-product. The requisite amount of the solution is then admixed with the required amounts of the additional ingredients water, ammonium nitrate prills, calcium nitrate, zinc oxide, acetic acid and sodium acetate, and the resulting admixture is heated at T5 6 1 under 55:56am mixing conditions. The required proportion of guar gum, as a dispersion in ethylene glycol, is then added to the above admixture followed by continued agitation and addition of the glass microballons and aluminum ingredients. After continued agitation to accomplish uniform admixing of all ingredients, a percent aqueous solution of the chromium acetate cross-linking agent- (see footnote 1 is added to, and uniformly mixed with, the above resulting ingredient mixture to form the final explosive ingredient mixture. Prior to completion of the crosslinking reaction, the product ingredient mixture is packaged for storage during which time crosslinking is completed to form the final firm gel product.

As will be evident to those skilled in the art, various modifications can be made or followed in light of the foregoing disclosure and discussion without departing from the spirit or scope of the disclosure or from the scope of the claims.

What I claim and desire to protect by Letters Patent 1. In a gelled aqueous slurry salt type explosive containing guar gum crosslinked with a chromium acetate, as a gelation agent, the improvement comprising calcium nitrate as at least part of the oxidizer salt component, and as said gelation agent guar gum crosslinked in the presence of at least part of said calcium nitrate at a pH of from about 4.5 to 5.4 with a chromium acetate of the group of chromium hydroxy diacetate, chromium triacetate, and mixtures thereof.

2. In a gelled explosive of claim 1, said explosive containing on a weight basis from 0.1 to 1.5 percent of said guar gum and from 0.01 to 0.5 percent of said chromium acetate crosslinked with said guar gum in the presence of at least 5 percent of said calcium nitrate at a pH of from 4.7 to 5.2.

3. in a gelled explosive of claim 2, said calcium nitrate constituting at least 10 percent of said oxidizer salt component.

4. A gelled explosive of claim 3, comprising from 5 to percent water, from 5 to 30 percent calcium ni- 6. An explosive of claim 4 wherein said crosslinking 7 agent is chromium triacetate.

7. In a process for the manufacture of a gelled aqueous salt slurry type explosive containing guar gum crosslinked with a chromium acetate, as a gelation agent, the improvement comprising incorporating calcium nitrate into said explosive as at least part of the oxidizer salt of said explosive, and effecting the gelation by crosslinking said guar gum with a chromium acetate of the group of chromium hydroxy diacetate, chromium triacetate, and mixtures thereof in the presence of at least part of said calcium nitrate and at a pH of about 4.5 to 5.4.

8. In a process of claim 7, incorporating into said explosive, on a weight basis, at least 5 percent of said calcium nitrate as at least part of said oxidizer salt.

9. In a process of claim 8, incorporating into said explosive from 5 to 30 percent calcium nitrate, from 10 to percent ammonium nitrate and from 2 to 50 percent of a fuel including fuel-sensitizer, from 5 to 30 percent water, and as said gelation agent from 0.1 to 1.5 percent guar gum crosslinked with from 0.01 to 0.5 percent of said chromium acetate.

10. A process of claim 8 wherein said chromium acetate is a mixture of chromium hydroxy diacetate and chromium triacetate.

11. A process of claim 8 wherein said chromium acetate is chromium triacetate.

12. In a process of claim 9, decreasing the rate of said crosslinking by effecting same in the presence of additional acetate ion.

13. In a process of claim 9, effecting said crosslinking at a temperature of at least F.

@2 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3. 298. 091 MM Ma 1 1 C 1 W1 Inventor(s) Herbert G. Knight, Jr. (Case 6) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract of Disclosure, line 4, the

second occurrence should read that In the Abstract of Disclosure, the last sentence is missing. It should read Method for the manufacture of the above explosives is also provided.

Column 3, in the Table under Example No., last line Acetate Acid should read Acetic Acid Signed and sealed. this 9th day of July 1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. 7 C. MARSHALL DANN Attesting Officer Commissioner of Patents @2 3 UNITED STATES PATENT OFFICE v CERTIFICATE OF CORRECTION Patent No. 3, 798. 091 DI Marcu q 1 Q74.

Inventor) Herbert G. Knight, Jr. (Case 6) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Abstract of Disclosure, line 4, the

second occurrence should read that In the Abstract ofDisclosure, the last sentence is missing. It should read Method for. the manufacture of the above explosives is also provided.

Column 3, in the Table under Example No., last line Acetate Acid should read Acetic Acid Signed and sealed this 9th day of July 1974.

(SEAL) Attest:

MCCOY M. GIBSON, JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents 

2. In a gelled explosive of claim 1, said explosive containing on a weight basis from 0.1 to 1.5 percent of said guar gum and from 0.01 to 0.5 percent of said chromium acetate crosslinked with said guar gum in the presence of at least 5 percent of said calcium nitrate at a pH of from 4.7 to 5.2.
 3. In a gelled explosive of claim 2, said calcium nitrate constituting at least 10 percent of said oxidizer salt component.
 4. A gelled explosive of claim 3, comprising from 5 to 30 percent water, from 5 to 30 percent calcium nitrate, from 10 to 80 percent ammonium nitrate, from 2 to 50 percent of a fuel including fuel-sensitizer, and from 0.1 to 1.5 percent of said guar gum crosslinked with from 0.01 to 0.5 percent of said chromium acetate.
 5. An explosive of claim 4 wherein said crosslinking agent is a mixture of chromium hydroxy diacetate and chromium triacetate.
 6. An explosive of claim 4 wherein said crosslinking agent is chromium triacetate.
 7. In a process for the manufacture of a gelled aqueous salt slurry type explosive containing guar gum crosslinked with a chromium acetate, as a gelation agent, the improvement comprising incorporating calcium nitrate into said explosive as at least part of the oxidizer salt of said explosive, and effecting the gelation by crosslinking said guar gum with a chromium acetate of the group of chromium hydroxy diacetate, chromium triacetate, and mixtures thereof in the presence of at least part of said calcium nitrate and at a pH of about 4.5 to 5.4.
 8. In a process of claim 7, incorporating into said explosive, on a weight basis, at least 5 percent of said calcium nitrate as at least part of said oxidizer salt.
 9. In a process of claim 8, incorporating into said explosive from 5 to 30 percent calcium nitrate, from 10 to 80 percent ammonium nitrate and from 2 to 50 percent of a fuel including fuel-sensitizer, from 5 to 30 percent water, and as said gelation agent from 0.1 to 1.5 percent guar gum crosslinked with from 0.01 to 0.5 percent of said chromium acetate.
 10. A process of claim 8 wherein said chromium acetate is a mixture of chromium hydroxy diacetate and chromium triacetate.
 11. A process of claim 8 wherein said chromium acetate is chromium triacetate.
 12. In a process of claim 9, decreasing the rate of said crosslinking by effecting same in the presence of additional acetate ion.
 13. In a process of claim 9, effecting said crosslinking at a temperature of at least 100*F. 